Floppy drive heliostat

This is an ongoing project to build a heliostat from a floppy drive. Heliostats are used by solar arrays to track the sun. This mod uses the main logic board to control the head stepper motor. The board will power up with 5V and consumes 1Watt when the motor is running. There are a couple quirks to the motor operation since this a floppy drive; large head movements require a backtrack every so often. Luckily, this device doesn’t move too far or fast. Two sets of LEDs are wired on opposite sides of a reflective strip. They’re wired opposite each other so that the device will track back if it overshoots.

Normally inward pointing arrows indicate a photodiode, not a light emitting diode. But in this case it looks to me like they actually are LEDs. It is a little known fact that normal LEDs can also generate a voltage (with extrememly low current) when light hits them. They work best when illuminated with the same color light they emit. So for a test just take a digital multimeter and connect a LED to the leads, and put it on voltage scale. Light another led and shine the light on the one connected to me meter. The meter should read a small amount of voltage.

IMWeasel is right. LEDS are photodetectors are LEDs, just that photodetectors are optimized for that, and LEDs tend to create light that is in a useful visible range — though there are LEDs that are made especially for use with a corresponding IR photodetector. In some devices you’ll find the IR photodetectors even look like LEDs. (Speakers, motors, thermocoolers — lots of other stuff works backwards too.)

However the multimeter reading will be off, FWIW. Multimeters generally have a input resistance somewhere around the 50K-100K and that brings the voltage down. The only way to know how many LEDs/detectors to stack up on a CMOS gate is to test them directly. With sunlight possibly you could get away with 1 yellow — I used two because as a night owl I needed to test on a lightbulb and one wasn’t cutting it.

BTW, in case you guys want to know, so far you’ve chewed through about 2/3rds of the 1G filehigh bandwidth I offloaded the pictures to and there’s still > 1 hit a minute. You people really don’t sleep do ya :-) No worries. Next stop is photobucket.

this is a cool idea, a good free way to track the sun! there’s thousands of old discarded floppy drives lying around the planet. I’m guessing A floppy drive motor would be hard pressed to move anything larger than a square foot unless you geared the motor way down. or You could hook the wires that that normally go to the motor to some relays or power transistors to drive a bigger motor… This would probably require a larger power supply or a battery.

I have also been inventing some heliostats that use phototransistors or cds cells to determine the direction of the sun…not unlike the floppyostat. here’s the link if you want to check it out

Technically what you are describing is not a “heliostat”.
A heliostat re-directs light to a stationary and fixed
receiver. You are describing a single axis, or dual axis
if you control 2 axes, solar tracker. You are attempting
to keep your receiver “normal” to the sun.
I.e, always directly facing the sun.
This is not called a heliostat.

A heliostat redirects light to a stationary receiver.
Furthermore the geometry between the sun, mirror, and
receiver constantly change throughout the day. OK, a
special subset of heliostat geometries can redirect light
along the polar axis and generally are called “Coelostats”.

What you are describing is generally called a single axis
solar tracker. You are using a stepper motor to effect the
movement. This is laud able. I really admire your ingenuity

I ‘m a member of a BEAM robotics group. I and Wilf Rigter
have described a super simple stepper motor solar tracker
driver for stepper motors. See:http://www.redrok.com/beamcircuits.htm#7e2
This uses a single IC and 4 transistors.
OK, double this for 2 axes.

Some have asked about the use of LEDs as light sensors.
This works very well. I use clear cased green LEDs a solar
sensors. Green LEDs can produce about 1.7 volts. This is a
lot more than wimpy a silicon sensor. 1.7 volts can
directly drive CMOS logic gates without the use of OP-Amps.
Cool huh?

All semiconductor devices can act as light sensors.
The voltage is defined by the “color” of the light.
Einstein got a Nobel Prize for defining the relationship
between the color of the light and the resultant voltage.
Called the Einstein photo electric equation.
Silicon is about .55V.
Red LEDs at about 1.25V.
Yellow LEDs at about 1.4V.
Green LEDs at about 1.7V.
Blue just under 3V.

These exotic semiconductors are not cheap. So they will
not be used in solar panels. However they work just fine
as light sensors.